BEIRUT, July 21 -- The Israeli military called up reserve troops Friday and broadcast urgent radio warnings for civilians of battered southern Lebanon to leave "immediately" for relative safety north of the Litani River, adding to the growing indications that Israel is planning a large-scale ground operation to root out Hezbollah guerrillas and their missile caches.

Hezbollah, for its part, continued Friday sending rockets crashing into northern Israel, causing damage and injuries but no deaths.

In Washington, meanwhile, Secretary of State Condoleezza Rice announced plans to travel to the region next week for talks with Israeli and Palestinian leaders, and for a conference on the crisis in Rome on Wednesday with officials from Arab countries and the European Union. But she warned that the United States will not support a cease-fire that falls short of fully disarming Hezbollah and restoring Lebanese government control throughout Lebanon.

"What I won't do is go to someplace and try to get a cease-fire that I know isn't going to last," Rice told reporters at the State Department.

"A cease-fire would be a false promise if it simply returns us to the status quo, allowing terrorists to launch attacks at the time and terms of their choosing and to threaten innocent people, Arab and Israeli, throughout the region," Rice said. "That would be a guarantee of future violence."

As she spoke, a column of Israeli armor and troops assembled on the border, where elite Israeli squads increasingly have been crossing over and engaging Hezbollah fighters in sharp but isolated clashes supported by tank and artillery fire. A Lebanese security official told reporters in Beirut that the Israeli soldiers have been moving in and out of Lebanese territory along a front stretching from Naqoura on the Mediterranean coast to Maroun al-Ras about 25 miles to the east, and on toward Majidiyeh to the north.

Two volleys of Hezbollah's longer-range rockets hit Haifa, a port city about 18 miles south of the border, and Israeli officials said 10 projectiles slammed into an apartment building and a post office. Three people were wounded and 16 were treated for shock, they said. Air raid sirens sounded throughout the day.

Rockets also exploded into a dozen other northern Israeli towns and farming villages, officials said, but no serious casualties were reported. In all, about 35 rockets came in. Hezbollah, a militant Shiite Muslim group, has fired more than 900 rockets into Israeli territory since the confrontation began July 12. Fifteen Israeli civilians have been killed and dozens wounded in the rocket attacks.

Four Israeli soldiers were killed late Thursday just north of the Israeli border town of Avivim, about 22 miles inland from the Mediterranean coast, during a mortar attack and intense firefight with Hezbollah guerrillas, the Israeli military said. That brought to 19 the number of Israeli soldiers killed in 10 days of fighting.

The Israeli army casualties have been greeted by many Lebanese as a sign of military prowess by Hezbollah fighters and preparedness by the militia leadership to confront Israeli forces. Hezbollah has acknowledged only six of its militiamen killed -- although Israel puts the number at 100 -- and its leader, Hasan Nasrallah, vowed in a television interview Thursday night to keep up the fight as long as Israeli attacks continue on Lebanese territory.

Lebanese President Emile Lahoud said in a television interview that the national army would defend the country if Israeli troops invade. In fact, the Lebanese army has stayed out of the conflict and has no substantial presence in the southern Lebanese hills where the fighting has occurred.

A United Nations observation post in Israel just south of the border was severely damaged in an attack that Israel blamed on stray Hezbollah rockets. But an unnamed U.N. officer told the Associated Press the destruction was caused by misdirected Israeli artillery fire. None of the Ghanian soldiers manning the post was injured, the officer said.

Israeli warplanes also Friday struck Hezbollah targets near Al-Khiam and carried out repeated raids in and around Baalbek in the lush Bekaa Valley to the northeast. Al-Jazeera, the Qatar-based news network, reported five civilians were killed and 20 were wounded, adding to a civilian death toll estimated by the Lebanese Health Ministry at more than 340.

Israeli jets also blasted three buses at the Lebanese-Syrian border that had just dropped off passengers fleeing to Damascus. Lebanese security officials said no one was injured. In all, Israeli warplanes carried out about 60 sorties, a military spokesman in Tel Aviv said.

The Beirut-Damascus highway, a vital artery for Lebanon's economy, has come under repeated attack by Israeli warplanes, forcing travelers to take back routes over the jagged mountains. Jets firing volleys of air-to-ground missiles Friday further damaged a key bridge connecting two steep hillsides that had shaved half an hour off the trip between the two capitals. The bridge's 1.6-mile span, the country's longest, was completed only several years ago and was regarded as a particularly proud symbol of Lebanon's recovery from the destruction of previous wars.

The Israeli military did not specify how many reserve soldiers would have to report for duty in the new call-up. But Maj. Gen. Udi Adam, head of the northern command, said it was "not an all-out, comprehensive mobilization."

Military officials, speaking on background, said initially at least the call-up would affect three battalions, which a spokesman said amounts to "several thousand" soldiers. Most will be assigned to the West Bank and Gaza, they said, to free better-trained full-time soldiers for duty along the Lebanese border.

Lt. Gen. Dan Halutz, the Israeli army chief of staff, told a news conference that Israel will do what is necessary to stop attacks from Hezbollah. That may include, he said, "limited ground operations as much as needed."

Capt. Noa Meir, a military spokeswoman, said the call-up and warnings to southern Lebanese civilians do not "necessarily mean that ground operations will get larger, but we have the option to do so, and if needed, we will."

Israel withdrew from southern Lebanon six years ago after a deeply unpopular 18-year-long occupation to enforce a buffer zone designed to keep Palestinian guerrillas and Hezbollah fighters away from Israel's northern border and keep their short-range missiles out of range. Apparently mindful of that memory, Adam, head of the Israeli northern command, said his forces do not intend to reoccupy the 12- to 20-mile-deep buffer zone, which Israel controlled from well before the 1982 invasion until the withdrawal in 2000. "Lebanon is Lebanon, and Israel is Israel," he said. But he added, "When normal life is disturbed, we need to neutralize the damage that is being caused to the population here."

A poll in Friday's Maariv newspaper showed overwhelming support for the war among Israeli citizens. Of those queried, 95 percent said the Israeli military campaign was justified and 90 percent said the attacks should continue until Hezbollah is pushed back from the border.

The poll also showed surging support for Prime Minister Ehud Olmert, with 78 percent voicing satisfaction with his leadership compared with 43 percent before the conflict began.

An Israeli radio station, al-Mashriq, repeatedly broadcast warnings to the civilian population of southern Lebanon, ordering people to flee northward. Israeli forces are determined to act, the radio said, and "therefore all residents of south Lebanon south of the Litani must leave their areas immediately for their own safety." Planes dropped leaflets with the same warnings, residents said.

Israeli warplanes have been firing on civilian cars and other vehicles regularly since the conflict began, and Lebanese trapped in the south said they feared they could become targets if they heed the warnings to flee. The French foreign minister, Philippe Douste-Blazy, said during a visit to Beirut that France wants to open an air and sea supply line for delivery of relief to besieged Lebanese civilians. He demanded that Israeli forces agree to respect a "humanitarian corridor" that would allow international aid to reach the estimated 500,000 Lebanese who have been driven from their homes during the past 10 days of warfare.

A Greek warship in Beirut to pick up Greek nationals fleeing the fighting brought in boxes of aid supplies and unloaded them at the port. It was unclear whether the aid would reach the people who need it in southern Lebanon, however, because Israeli air attacks have made travel down the coastal road highly dangerous.